Implement a GetRoleBindings() feature

[Will Moorby]

Describe the solution you'd like
Very simple. Just to create GetRoleBindings() function that can be used just like the GetRole() function.

Describe alternatives you've considered
I haven't considered any alternatives as I think this is a really simple task, just need to plug things in really.

Additional context
Was writing some tests and realised that this function doesn't actually exist. I had a quick look at how GetRole() is implemented and I think this GetRoleBinding() function can be implemented in the exact same way. I had a look at the contribution docs and I believe this is something I can do quite easily. See below for a description of "plugging things in" as I said earlier.

Here's the GetRole() functions:

package k8s

import (
	"context"

	"github.com/gruntwork-io/terratest/modules/testing"
	"github.com/stretchr/testify/require"
	rbacv1 "k8s.io/api/rbac/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

// GetRole returns a Kubernetes role resource in the provided namespace with the given name. The namespace used
// is the one provided in the KubectlOptions. This will fail the test if there is an error.
func GetRole(t testing.TestingT, options *KubectlOptions, roleName string) *rbacv1.Role {
	role, err := GetRoleE(t, options, roleName)
	require.NoError(t, err)
	return role
}

// GetRoleE returns a Kubernetes role resource in the provided namespace with the given name. The namespace used
// is the one provided in the KubectlOptions.
func GetRoleE(t testing.TestingT, options *KubectlOptions, roleName string) (*rbacv1.Role, error) {
	clientset, err := GetKubernetesClientFromOptionsE(t, options)
	if err != nil {
		return nil, err
	}
	return clientset.RbacV1().Roles(options.Namespace).Get(context.Background(), roleName, metav1.GetOptions{})
}

The RbacV1() function (see final return in above code block) returns the RbacV1Interface. This interface includes a return function for the RoleBindingInterface:

type RbacV1Interface interface {
	RESTClient() rest.Interface
	ClusterRolesGetter
	ClusterRoleBindingsGetter
	RolesGetter
	RoleBindingsGetter
}

// RbacV1Client is used to interact with features provided by the rbac.authorization.k8s.io group.
type RbacV1Client struct {
	restClient rest.Interface
}

func (c *RbacV1Client) ClusterRoles() ClusterRoleInterface {
	return newClusterRoles(c)
}

func (c *RbacV1Client) ClusterRoleBindings() ClusterRoleBindingInterface {
	return newClusterRoleBindings(c)
}

func (c *RbacV1Client) Roles(namespace string) RoleInterface {
	return newRoles(c, namespace)
}

func (c *RbacV1Client) RoleBindings(namespace string) RoleBindingInterface {
	return newRoleBindings(c, namespace)
}

Therefore, I can just create 2 new functions for GetRoleBinding that look something like this (just writing this up quickly before I go to sleep, so I'm not confident this is correct, just giving any readers the main idea):

// GetRoleBinding returns a Kubernetes roleBinding resource in the provided namespace with the given name. The namespace used
// is the one provided in the KubectlOptions. This will fail the test if there is an error.
func GetRoleBinfing(t testing.TestingT, options *KubectlOptions, roleBindingName string) *rbacv1.RoleBinding {
	role, err := GetRoleBindingE(t, options, roleName)
	require.NoError(t, err)
	return role
}

// GetRoleBindingE returns a Kubernetes roleBinding resource in the provided namespace with the given name. The namespace used
// is the one provided in the KubectlOptions.
func GetRoleBindingE(t testing.TestingT, options *KubectlOptions, roleBindingName string) (*rbacv1.RoleBinding, error) {
	clientset, err := GetKubernetesClientFromOptionsE(t, options)
	if err != nil {
		return nil, err
	}
	return clientset.RbacV1().RoleBindings(options.Namespace).Get(context.Background(), roleName, metav1.GetOptions{})
}

As I've already said, I'd be happy to do all the work for this improvement, I've a brief glance at the contribution docs already.